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  <div class="titlepage"><div><div><h1 style="clear: both">Prerequisites</h1></div></div></div>
<p>Outcome is a header-only C++ 14 library known to work well on the latest
point releases of these compiler-platform combinations or better:</p>

<ul>
<li>clang 4.0.1 (LLVM) [FreeBSD, Linux, OS X]</li>
<li>GCC 6.5 [Linux]</li>
<li>Visual Studio 2017.9 [Windows]</li>
<li>XCode 9 [MacOS]</li>
</ul>

<p>For non-Windows non-POSIX platforms (typically embedded systems), Outcome
is usable in its Outcome.Experimental form with the macro <code>BOOST_OUTCOME_SYSTEM_ERROR2_NOT_POSIX</code>
defined.</p>

<p>It is worth turning on C++ 17 or C++ 20 if you can, as there are many usability and
performance improvements. Any Concepts TS or Coroutines TS implemented
by your compiler is automatically detected and used.</p>

<p>Partially working compilers (this was last updated January 2019):</p>

<ul>
<li>clang 3.5 - 3.9 can compile varying degrees of the test suite, the
problem is lack of complete and unbuggy C++ 14 language support.</li>
<li>Older point releases of GCCs 7 and 8 have internal compiler error bugs
in their constexpr implementation which tend to be triggered by using
Outcome in constexpr. If you don&rsquo;t use Outcome in constexpr, you won&rsquo;t
see these problems. If you need your GCC to not ICE, upgrade to the
very latest point release, the constexpr ICE has been since fixed.</li>
<li>Early editions of Visual Studio 2017 have many corner case problems.
The latest point release, VS2017.9, only has a few known problems,
and should be relatively unsurprising for most use cases.</li>
</ul>

<hr />

<p>&ldquo;C++ 14&rdquo; compilers which do not work, and will not work until their
maintainers fix them:</p>

<ul>
<li>GCC 5, due to a bug in nested template variables parsing which was fixed
in GCC 6. I appreciate that this upsets a lot of users. Please raise your
upset at <a href="https://gcc.gnu.org/bugzilla/">https://gcc.gnu.org/bugzilla/</a>. In the meantime, you can get fairly
far in Outcome with even clang 3.5.</li>
<li>Any compiler which uses the libstdc++ version which comes with GCC 5, as it does
not implement enough of the C++ 14 standard library for Outcome to compile.</li>
</ul>



        </div><p><small>Last revised: February 25, 2020 at 11:15:13 UTC</small></p>
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